1. Field of the Invention
The present invention relates to a wheel bearing device for rotatationally supporting a drive wheel relative to the body of an automobile. More specifically, the present invention relates to a bearing device for a drive wheel of the type that includes a hub wheel, a constant velocity universal joint and bearings arranged in rows. In the present invention the hub wheel, the universal joint and the bearings are unitized and the plurality of inner races of the bearings are partially formed in the outer joint member of the constant velocity universal joint on one side.
2. Description of the Related Art
The drive wheels of automobiles including the rear wheels of FR cars, the front wheels of FF cars and all the wheels of 4WD cars are supported in suspension by means of a bearing device for a drive wheel. Known bearing devices for a drive wheel include the one disclosed in Japanese Patent Laid-Open Publication No. Hei. 11-62951.
Referring to FIG. 12 of the accompanying drawings, the bearing device disclosed in the above patent document includes a hub wheel 10, a bearing unit 20 and a constant velocity universal joint 30 that are unitized. One of the paired inner races 12 is formed in the hub wheel 10 while the other one 42 is formed in the outer joint member 40 of the constant velocity universal joint 30. The hub wheel 10 and the outer joint member 40 are coupled to each other by mutual engagement of the female spline 53 and the male spline 55 and caulking the axial end of the outer joint member 40 that is projecting from the hub wheel 10. The female spline 53 is formed on the inner peripheral surface of the hub wheel 10, and the male spline 55 is formed on the outer peripheral surface of the outer joint member 40. Additionally, the male spline 55 of the outer joint member 40 of the bearing device is provided at the opposite lateral sides thereof with cylindrical surfaces 77 and 79 to improve its flexural rigidity or the like. The surfaces 77 and 79 are then engaged with the tooth-front surface of the female spline 53 of the hub wheel 10.
With the structural arrangement of FIG. 12, the cylindrical surfaces and the tooth-front surface of the female spline 53 have to be brought into mutual engagement without any play. Therefore, both the cylindrical surfaces and the tooth-front surface are required to show an enhanced level of precision particularly in terms of coaxial arrangement. Then, both the outer joint member and the hub wheel including their respective splines need to be accurately machined and consequently the manufacturing cost is raised.
In view of the above-identified circumstances, it is therefore an object of the present invention to improve the strength of coupling the hub wheel and the outer joint member of a bearing device for a drive wheel without significantly raising the manufacturing cost.
According to the present invention, the above object is achieved by providing a bearing device for a drive wheel including a hub wheel, a constant velocity universal joint and bearings arranged in rows, the hub wheel, the universal joint and the bearings being unitized, the plurality of inner races of the bearings being formed partly in the outer joint member of the constant velocity universal joint at a side thereof, the hub wheel and the outer joint member being meshed with each other by way of torque transmission means and coupled to each other by caulking, plastic deformation caused by the caulking supporting the torque transmission means at near the caulked section. As a result of this appropriation, any peripheral play between the hub wheel and the outer joint member can be minimized to improve the strength of coupling them. While any appropriate means may be used for the caulking, the caulking can be realized particularly effectively and efficiently by using a rocking technique.
Furthermore, the above object is also achieved by providing a bearing device for a drive wheel including a hub wheel, a constant velocity universal joint and bearings arranged in rows, the hub wheel, the universal joint and the bearings being unitized, the plurality of inner races of the bearings being formed partly in the outer joint member of the constant velocity universal joint at a side thereof, the hub wheel and the outer joint member being meshed with each other by way of torque transmission means and coupled to each other by caulking, undulations of said torque transmission means at near a caulked section being filled with plastic deformed part caused by said caulking.
Preferably, a bearing device for a drive wheel according to the invention includes the aforementioned caulked section at one end of the torque transmission means in an axial direction and an engaging section engaged at the other end with the hub wheel and the outer joint member without play. Then, the engaging section is tightly engaged in such a way that there is no play between the hub wheel and the outer joint member so that it operates to satisfactorily bear the radial load of the device.
Preferably, the torque transmission means comprises serrations, which may be splines.
When tightly coupling the outer joint member and the hub wheel by caulking, the outer joint member may be engaged at the corresponding axial end thereof with the hub wheel by caulking or alternatively the hub wheel may be engaged at the corresponding end thereof with the outer joint member by caulking.
The axial end of the stem that is to be caulked needs to show ductility to a certain extent. Therefore, preferably, the caulked section is made to show the hardness of the material prior to heat treatment.
When the outer joint member is caulked at the axial end thereof and brought into engagement with the hub wheel, the outer joint member is preferably provided at the axial end with a section to be caulked having a diameter smaller than that of the groove of its serration.
Then, preferably, the serration of the outer joint member is made to show a cut-out profile at the corresponding axial end thereof. With such a profile, the shearing load can be prevented from concentrating and any possible cracks in the caulked section can be avoided when the serration of the outer joint member is made to have the axial end of the bottom of the groove thereof located at the inboard side relative to the corresponding end face of the hub wheel.
Preferably, the serration-engagement of said outer joint member and that of said hub wheel is realized by interference at least at the side opposite to the axial end. When the torque transmission means is provided at and near the caulked section by plastic deformation caused by caulking as described above, the torque is largely borne by the plastically deformed section because the outer joint member and the hub wheel bite each other in the plastically deformed section to eliminate any play therebetween. On the other hand, when the serration-engagement of the outer joint member and the hub wheel is realized by interference at the side opposite to the axial end, the torque is also borne by the interfering section to consequently reduce the torque borne by the plastically deformed section and avoid any possible cracks in the caulked section.
The efficiency of causing the serrations to engage each other can be improved by realizing the serration-engagement by means of clearance fit at the axial end side.
The interference can reliably be formed by tilting either the serration of the outer joint member or that of the hub wheel relative to the axial direction. Alternatively, the interference can be formed by tilting either the serration of the outer joint member or that of the hub wheel relative to the axial direction at the side opposite to the axial end and formed in parallel with the axial direction at the axial end side relative to that side.
The torque transmission means may be formed by arranging undulations on the engaging surfaces of the hub wheel and the outer joint member and caulking the engaging surfaces by at least partly enlarging or reducing the diameters of the engaging surfaces including the undulations. With such an arrangement, the undulations bite the engaging surfaces of the partner members so that the torque can be transmitted by way of the hub wheel and the outer joint member and the strength of coupling the hub wheel and the outer joint member can be improved in order to prevent the caulked section from becoming loose for a long period of time. Undulations may be formed on either or both of the engaging surfaces of said hub wheel and said outer joint member.
The undulations can withstand any efforts trying to crush them and bite the engaging surfaces of the partner members to establish a strengthened plastic coupling effect when they are hardened by heat treatment.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.